One key aspect of the efficient operation of PVRs (Personal Video Recorders) that record a digital television signal is the ability to quickly, easily, and reliably identify places within a recorded video stream that correspond to starts and ends of pictures, locations of certain picture types, and a time associated with a picture. All of the places within the recorded video stream that correspond to the starts and ends of pictures; locations of certain picture types; and time associated with the picture are typically carried as part of the digital video signal. However, the digital television signal is often encrypted (also termed “scrambled” in the art and throughout the present specification and claims) in order to ensure correct payment for access to the television signal. It is often desirable not to decrypt the television signal when the television signal is recorded; accessing the places within the recorded video stream that correspond to the starts and ends of pictures; locations of certain picture types; and time associated with the picture is therefore difficult. Even if the signal is decrypted upon recording, or is transmitted unencrypted, locating desired information can require searching through large amounts of the digital television signal, which can be a costly operation.
It is appreciated that while the following discussion concentrates on video based systems, the present invention can also be applied to other coding technologies such as audio or data coding systems. The use of the word “video” should not be taken as limiting the scope of the invention.
Newer video coding technologies, such as AVC (ISO/EEC 14496-10) make it even more important that the information is correctly signalled, since existing heuristic mechanisms for “guessing” the location, value and type of information are becoming ever more unreliable due to the changes in video coding technologies.
Digital video standards that are relevant to understanding the state of the art include the following published standards:    ISO/EEC 13818-1:2000, MPEG-2 Systems Specification;     ISO/EEC 13818-2:2000, MPEG-2 Video Specification, particularly Sections 6.3.3 and 6.3.8;    ISO/EEC 13818-1:2000/Amd.3:(2003), Transport of AVC video data in MPEG-2 TS;     ISO/IEC 14496-10:2003 MPEG-4 AVC Video Specification, particularly Sections 7.3.1, 7.4.1, Annex A, D.8.7, and D.9.7; and    Annex E of ETSI TS 101 154 V1.5.1 (2004-05), Digital Video Broadcasting (DVB); Implementation guidelines for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream.     Internet Engineering Task Force (IETF) Requests for Comment (RFCs) that are relevant to understanding the state of the art include the following published RFCs:    RFC 1889, RTP: A Transport Protocol for Real-Time Applications; and    RFC 1890, RTP Profile for Audio and Video Conferences with Minimal Control. 
The following patent applications are believed to represent the state of the art:    PCT Patent Application PCT/IL00/00276 (published as WO 01/35669) of NDS Limited, and corresponding U.S. patent application Ser. No. 09/574,096 of Darshan et al; and    PCT Patent Application PCT/IL02/00534 (published as WO 03/010970) of NDS Limited, and corresponding U.S. patent application Ser. No. 10/479,373 of Darshan et al.
The disclosures of PCT Patent Application PCT/IL00/00276 (published as WO 01/35669) of NDS Limited, and corresponding U.S. patent application Ser. No. 09/574,096 of Darshan et al and PCT Patent Application PCT/IL02/00534 (published as WO 03/010970) of NDS Limited, and corresponding U.S. patent application Ser. No. 10/479,373 of Darshan et al. are hereby incorporated herein by reference.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.